Manipulation of filaments

ABSTRACT

A PROCESS FOR THE PRODUCTION OF AN ASSEMBLY OF ORIENTED STAPLE FIBERS WHICH COMPRISES FEEDING A DISPERSION OF STAPLE FIBERS IN A LIQUID MEDIUM AT A RATE SUCH THAT LAMINAR FLOW CONDITIONS ARE EXPERIENCED, ONTO A PERFORATE SURFACE THROUGH WHICH THE LIQUID MEDIUM MAY PASS BUT ON WHICH THE STAPLE FIBERS ARE REATAINED, SO THAT THE STAPLE FIBERS LIE ON THE PERFORATE SURFACE SUBSTANTIALLY AT RIGHT ANGLES TO THE DIRECTION OF FLOW OF THE DISPERSION. THE ASSEMBLY OF FIBERS MAY BE REMOVED FROM THE PERFORATE SURFACE IN THE FORM OF A COHERENT LAYER OF FIBRES, AND MAY BE USED, FOR EXAMPLE, FOR THE PRODUCTION OF RESIN COMPOSITES.

sept- 12, 1972 D. w. GROOMBRIDGE MANIPULATION OF FILAMENTS Filed Nov. 18, 1969 FIG./

United States Patent M US. Cl. 156-621 7 Claims ABSTRACT OF THE DISCLOSURE A process for the production of an assembly of oriented staple fibres which comprises feeding a dispersion of staple fibres in a liquid medium at a rate such that laminar flow conditions are experienced, onto a perforate surface through which the liquid medium may pass but on which the staple fibres are retained, so that the staple fibres lie on the perforate surface substantially at right angles to the direction of flow of the dispersion. The assembly of fibres may be removed from the perforate surface in the form of a coherent layer of fibres, and may be used, for example, for the production of resin composites.

This invention relates to a process for the manipulation of filaments and is particularly concerned with the production of oriented assemblies of staple fibres.

Staple fibres which are to be used for the impregnation of plastics materials or other products for purposes of reinforcement may sometimes be employed in random or semirandom arrangements but for many purposes it may be desired to have the majority of the filaments arranged in one direction. Thus, for example when staple fibres produced from filamentary carbon are to be used as reinforcing materials in plastics composites it is extremely desirable that the filaments should mostly be oriented in the same direction and it is to this application that the present invention is most particularly directed. However, it will be understood that it may be employed wherever an assembly of unidirectionally oriented staple fibres is required.

According to the invention a process for the production of an assembly of oriented staple fibres comprises feeding a dispersion of staple fibres in a liquid medium at a rate such that laminar flow conditions are experienced, on to a perforate surface through which the liquid medium may pass but on which the staple fibres are retained, so that the staple fibres lie on the perforate surface substantially at right angles to the direction of flow of the dispersion.

The invention is based upon the discovery that when fibres of staple length which are carried in a liquid showing laminar flow characteristics impinge on a perforate surface they tend to arrange themselves in an alignment which is perpendicular to the direction of flow.

A dispersion of staple fibres for use in the invention may be made for example by feeding the staple fibres into a flow of turbulent liquid which liquid is preferably water but may be any other liquid which is inert to the material of the fibres. After dispersion of the fibres in the liquid the flow conditions are adjusted so that turbulence ceases and the dispersion of fibres may be directed in laminar flow through a pipe, for example, or over a weir or series of weirs.

Staple fibres which may be used in the process of the invention include natural fibres such as cotton, linen or wool and man-made fibres such as for example viscose rayon, acetate, nylon, polyester or polyacrylic fibres. In a preferred form of the invention the feed material consists of a dispersion of filamentary carbon of staple length which is preferably derived from a high temperature treatment of man-made fibres consisting wholly or mainly of polyacrylonitrile. If the fibres are not readily wetted 3,690,975 Patented Sept. 12, 1972 by the dispersing liquid it may be desirable to employ a wetting agent.

In one form of the invention a dispersion of carbon fibres in water may be fed through a pipe in which it may be allowed to flow on to a perforate surface, such as a gauze of metal or textile material, which perforate surface is moving relative to the pipe in a direction at right angles to the flow of the liquid dispersion in the pipe. Thus, for example the perforate surface may itself be moving in the required direction and may if desired be a continuous belt passing over guide rollers from which the assembly of fibres may be continuously removed. Alternatively in order to prepare relatively short assemblies of fibres the perforate surface may be stationary and the pipe carrying the dispersion of fibres may be moved along it in the required direction. If a wide assembly of fibres is required a plurality of pipes may be employed which discharge over a substantial width of the perforate surface, or one pipe may make several traverses.

In a preferred form of the invention which can give a high degree of fibre orientation, the dispersion of fibres is fed over a Weir or an inclined plate which is arranged so that the dispersion discharges onto the perforate surface with a relatively small fall and without excessive turbulence to avoid disturbance of the fibres on the perforate surface. Such a weir or plate may be flat, fluted, corrugated or stepped to improve the distribution of the fibres in the dispersion across its width and to improve the alignment of the fibres while flowing, and on the perforate surface. A multiple weir or plate consisting of a number of sections in echelon may be used to spread the total flow over a larger area to minimise turbulence on the perforate surface. The perforate surface itself may be employed horizontally or it may be inclined to improve drainage of the liquid.

Two or more layers of oriented filaments may be laid together, if desired, and successive layers may have their filaments oriented in different directions, for example, at right angles to one another.

The invention may also be employed to produce a pad of radially oriented fibres, by depositing them on a rotating perforate surface. Such a pad is useful in the production of, for example, bearings reinforced with filamentary material, such as carbon filaments.

Assemblies of filaments made by the process of the invention are of value as non-woven fabrics, and may, if desired be bonded with resins or other bonding materials to give them additional strength. Such assemblies of filaments are, however, especially of value in the production of composite materials, in which, for example, carbon or graphite fibres are incorporated in a resin matrix. The invention also includes composites made in such a manner.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawing, in which FIG. 1 is a schematic sectional elevation of an apparatus for carrying out the process of the invention in which the dispersion is fed through a pipe onto the perforate surface, and

FIG. 2 is a schematic sectional elevation of a modified form of the apparatus of FIG. 1 in which the feed is by way of a weir.

Referring to FIG. 1, a trough l is fed with water from a pipe 2 and with carbon fibres of staple length from a hopper 3 to form a dispersion 4, which discharges over a weir 5 into a tank 6. The dispersion emerges from the tank 6 through a pipe 7 at a sufficiently low rate to maintain laminar flow in the pipe 7, and falls onto the upper flight of an endless perforated belt 8, which passes over spaced-apart, horizontally disposed rollers 9 and 10, at least one of which is driven by drive means (not shown). A mat of carbon fibres 11 is deposited on the belt 8, and the water passes downwardly through the perforations. The mat is taken off the belt by a guide plate 12 and is rolled up on a roller 13.

FIG. 2 shows a modification of the apparatus of FIG. 1, in which the tank 6 has a weir outlet 14 which discharges over a slanting plate outfall from which the dispersion is fed directly to the perforated belt 8. The remainder of the apparatus is similar to that shown in FIG. 1.

The invention is further described in the following examples.

EXAMPLE 1 A dispersion of carbon fibres was prepared by feeding a mixture of gms. of filamentary carbon of 4.5 cms. staple length into 135 litres of water and circulating the mixture through a rotary pump. The dispersion was fed at a rate of 18 litres per minute through a 2.5 cms. diameter pipe terminating in a spade shaped feed plate on which the dispersion formed a stream of approximately 10 cms. in width with laminar flow characteristics. The dispersion was allowed to stream on to a horizontal gauze of 12 mesh per lineal cm. which was moved substantially at right angles to the direction of flow. A tape of carbon fibres was obtained in which the fibres were substantially oriented in the direction of movement of the gauze.

EXAMPLE 2 The conditions of Example 1 were followed but the gauze was folded along its length in such a manner as to cause the fibres to align and collect along the fold in the form of a roving of substantially unidirectional fibre orientation.

EXAMPLE 3 A dispersion of 50 gms. of 1 cm. carbon fibres in 135 litres of water was fed to a cms. wide gauze by way of an inclined feed plate which consisted of a flat sheet 61 cms. long by 35.5 cms. wide in such a manner that the dispersion streamed in laminar fiow over the full width of the gauze. The feed plate was reciprocated along the length of the gauze to form a fibre mat of 60 cms. by 30 cms. with a dry weight of 280 gms. per square metre.

The mat obtained in this example was formed into a laminate using an epoxy resin matrix. 16 layers of 11.5 cms. by 2.5 cms. were moulded together to form the laminate with the length of the layers parallel with the alignment of the fibres. A similar laminate was made by having the fibres oriented in the other direction. The laminate in which the fibres were aligned along the length had a tensile modulus value 2.5 times that of the other laminate.

EXAMPLE 4 A dispersion of 100 gms. of 2 cms. carbon fibres in 135 litres of water was fed down an inclined feed plate as in Example 3 to produce a pad of fibres in an area of 30 cms. by 15 cms. and having a dry weight of approximately 2 kgs. per square metre. The fibres in the felt were found to be oriented substantially completely in the direction perpendicular to the line of flow.

EXAMPLE 5 A dispersion of carbon filaments as used in Example 4 was fed down a channel 3.8 cms. wide to impinge on a radius of a slowly rotating disc of wire gauze. The filaments collected in a radial formation to form a pad suitable for use in laminates for bearings.

What is claimed is:

1. A process for the production of an assembly of oriented staple fibres which comprises the steps of:

dispensing staple fibres in a liquid medium;

feeding the dispersion onto a perforate surface through which the liquid may pass and on which the staple fibres are retained; and

controlling the rate of flow of the dispersion onto the perforate surface to provide laminar flow conditions, so that the retained staple fibres lie on the perforate surface at right angles to the direction of flow of the dispersion.

2. The process as claimed in claim 1 in which the liquid medium is water.

3. The process as claimed in claim 1 in which the liquid medium contains a wetting agent.

4. The process as claimed in claim 1 in which the dispersion of staple fibres is fed through a pipe to the perforate surface, which perforate surface moves relatively to the discharge point from the pipe.

5. The process as claimed in claim 1 in which the dispersion of staple fibres is fed over a weir to the perforate surface, the fall of the weir being small enough to avoid excessive turbulence on the perforate surface.

6. The process as claimed in claim 1 including the additional step of removing the assembly of staple fibres from the perforate surface.

7. The process as claimed in claim 6 including the additional step of incorporating the removed assembly of staple fibres in a resin matrix.

References Cited UNITED STATES PATENTS 2,384,032 9/1945 Jackson 19-66 R X 2,418,126 4/1947 Spalding et a1 19-66 R 2,803,125 8/1957 Mesek 1966 R X 3,228,067 l/1966 Strang et al 19-66 R 3,377,220 4/1968 Berger et al 15662.2

FOREIGN PATENTS 74,564 1/ 1945 Czechoslovakia 156-622 BENJAMIN A. BORCHELT, Primary Examiner H. J. TUDOR, Assistant Examiner U.S. Cl. X.R. 1966 R; 156369 UNITED STATESiPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 0, 7 Dated September 12-, 1972 Inventor() ,DENIS WILLIAM GROOMBRVIDGE It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

$- In the heading, the following should appear; I t

Claims priority of British application 54848/68- filed November 19, 1968.

signed and sealed this 1st day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. f ROBERT GOTTSCHALK Attesting; Officer Commissioner of Patents 

